Exploration of the Atomic Pathway of Seed-Mediated Growth from Icosahedral [Au25(SR)18]− to Bi-Icosahedral Au38(SR)24 and Au44(SR)26 Clusters Based on the 2e– Hopping Mechanism

Abstract

Size growth is ubiquitous in the gold nanocluster synthesis. However, the atomic-level mechanism of seed-mediated growth of gold clusters remains mysterious. In this study, the seed-mediated growth pathway from the icosahedral [Au25(SR)18]- cluster to the bi-icosahedral Au38(SR)24 and Au44(SR)26 clusters is studied based on the two-electron (2e-) hopping mechanism. First, atomic structures of three key intermediate clusters, [Au29(SR)20]-, [Au33(SR)22]-, and Au41(SR)25, are predicted based on the 2e--unit decomposition strategy. The theoretically simulated UV-Vis spectra based on the predicted structure model of [Au29(SR)20]- and [Au33(SR)22]- matched well with the experimental curves reported previously. Based on the predicted intermediate cluster structures, the size growth pathway from the eight-electron (8e-) [Au25(SR)18]- cluster to 14-electron (14e-) Au38(SR)24 and 18-electron (18e-) Au44(SR)26 clusters is determined. In the step of formation of bi-icosahedral Au38(SR)24 from icosahedral [Au25(SR)18]-, two Au4 units are first formed. The third 2e- hopping step results in formation of an icosahedron unit. The present studies offered new insights into the formation and size conversion mechanism of ligand-protected gold nanoclusters containing icosahedral cores.